Transmission device



Aug. 19, 1941. MEcHuNc;

TRANSMISSION DEVICE Filed Jan. 18, 1940 INVENTOR E. B. MECHL INGATTORNEY Patented Aug. 19, 1941 UNITED STATES PATENT OFFICE TRANSMISSIONDEVICE Eugene B. Mechling, Scarsdale, N. Y., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication January 18, 1940,Serial No. 314,506

I 9 Claims.

I This invention relates to transmission devices and more particularlyto an input transformer for use in vacuum tube amplifier or repeatercircuits. V

An object of the invention is the improvement of transmission over aline which includes an amplifier or arepeater.

A more specific object of the invention is the reduction of distortionand other deleterious effects arising from the fiow of currents in thelongitudinal circuit of a; transmission line.

In the use of either open wire or cable circuits for communicationpurposes considerable difficulty is very often experienceddue to theproximity of power lines andother communication circuits. Induction fromsuch neighboring circuits often gives-rise to longitudinal voltages inthe communication circuit which may result in objectionable distortionand noise. Current fiow in the longitudinal circuit of .the communication circuit may be caused also by elements of the communicationcircuit itself such, for example, as the source of voltage provided forthe vacuum tube amplifiers.

A feature of the present invention comprises means readily appliedtoexisting components of the communication circuit whereby the eifects oflongitudinal voltages therein are nullified and noise and distortion areprevented.

In accordance with a specific embodiment of the invention a path toground through a suitable network, which may bea variable condenser, isconnected to an external terminal of the primary winding of the inputtransformer asso- Referring now to Fig. 1, a portion of a conventionalvacuum tube repeater circuitis illustrated comprising an inputtransformer l l', vacuum tube amplifier l2, output transformer l3 andthe usual potential sources viz. filament battery l4, grid biasingbattery I and plate battery [6. Terminal S2 of the secondary winding ofinput transformer II is connected to ground 21. The windings of inputtransformer II are in series aiding relationship when connected P1 to P2to Ps'to P4 to S2 to S1. Signaling currents receivedover incoming lineL1 are applied to amplifier l2 through input transformer H and areapplied in amplified form through output transformer I3 to outgoing lineL2 in the usual manner.

Terminal P4 of the primary winding of input transformer H is connectedto ground 22 over a path which includes variable condenser 23, this pathto ground throughthe variable condenser constituting the correctivemeans of the ciated with a vacuum tube amplifier or re- V peater;Provision of this path to ground results in setting up in the primarywinding 2. current which is effective to establish a voltage rise in thesecondary which offsets the voltage drop therein resulting from theaction of longitudinal currents passing through the interwindingcapacitance of the transformer to ground.

A complete understanding of the invention as well as appreciation of thevaluable features thereof maybe gained from consideration of thesubsequent detailed description in connection with the drawing in which:i

Fig. 1 shows a vacuum tube repeater circuit the input transformer ofwhich is provided with corrective means in accordance with features ofthe present invention; and

Fig. 2 shows a vacuum tube amplifier circuit the input transformer ofwhich likewise is provided with corrective means in accordance withfeatures of the present invention.

embodiment of the present invention disclosed in Fig. l. Condenser 23should be of relatively small capacity in order that the high frequencysignaling currents will not. be affected appreciably by this path toground. V

In order to describe the-operation of the corrective means, i. e., thepath to ground 22 through capacity -23, let us assume first that thiscorrective means be absent and that a longitudinal voltage has been setup in line L1 through inductive action. This longitudinal voltage willset up a longitudinal current between the pri-. mary and secondarywindings of input transformer H to ground 2i through the interwindingcapacitances of the transformer represented by the dotted capacitiesCPS]. and CPS2. This current results in an impedance drop in thesecondary winding of transformer II which impedance drop, if wearbitrarily choose the moment when the direction of current is from coilto ground, will be from terminal S1 to S2. This impedance drop is highlyundesirable as it re-' sults in distortion of the wave beingtransmitted.

Now let us see how the provision of the corrective means of the presentinvention, i. e.,the

path to ground 22 through capacity 23, acts to With a current in theprimary winding through condenser to ground 22. This current will resultin an impedance drop in the primary winding which, assuming the samecurrent direction as before, will be from terminal P1 to P4. Thisimpedance drop by transformer action, will result in a voltage rise inthe secondary winding from terminal 81 to S2. Thus a voltage rise isestablished in the secondary winding which opposes the drop resultingfrom the longitudinal current passing through the interwindingcapacities to ground 2!. By proper adjustment of condenser 23neutralization may be attained.

In view of the fact that provision of the corrective means describedabove involves merely connection of a simple network to one of theexternal terminals of the input transformer it will be apparent thatsuch corrective means can be readily and economically added to apparatusalready being used in the field. This is considered an especiallyvaluable feature of the invention as it has been applicants experiencethat longitudinal voltage troubles are often not foreseen when aparticular communication line is set up and, indeed, often arise onlywhen power lines and the like are subsequently established in proximityto the communication circuit.

Referring now to Fig. 2, a vacuum tube amplifier circuit is disclosedincluding vacuum tube amplifier III, input transformer H2 and-outputtransformer H3. Amplifier tube III is provided with cathode H4, grid H5and anode H6. Cathode II 4 is energized by battery III- over a pathtraced from battery I I1, conductor I2I, cathode H4, resistance I22 toground 523; when the amplifier is in operation battery I I I alsosupplies potential to anode I I 6 over a path traced from battery I I1,conductor I2I, cathode H4, through the space charge path of the vacuumtube to anode H6, primary winding I24 of output transformer I I3, chokecoil I25 to ground I23. The windings of input transformer II 2 are inseries aiding relationship when connected P1 to P2 to S1 to S2.Signaling currents received over incoming line L1 are applied toamplifier tube III through input transformer I I2 and are applied inamplified form through output transformer I I 3 to outgoing line L2 inthe usual manner.

Wire-to-ground capacitance of the incoming line is represented bycondensers MI and I42 and ground I43.

Terminal P2 of input transformer I I2 is connected to ground I44 over apath which includes variable condenser I45, switch I46 and contact I41,this path to ground through the variable condenser constituting thecorrective means of the embodiment of the invention illustrated in Fig.2. Condenser I45 should be of relatively small capacity in order thatthe high frequency signaling currents will not be affected appreciablyby this path to ground.

In order to describe the operation of the corrective means disclosed inFig. 2 let us assume first, as we did in the description of Fig. 1,above, that the corrective means be absent. A current which We willrefer to as the noise current will beset up, by any noise voltage whichmay exist across battery I I1, between the primary and secondarywindings of input transformer I I2 due to the interwinding capacitancesrepresented by the dotted capacities C1=s1 and CPS2 and will flow overconductors I 5I and I52 respectively, of incoming line L1 to ground I43.This noise current results in an impedance drop in the secondary windingof input transformer H2 which impedance drop, if we arbitrarily choosethe moment when the noise voltage is inthe direction indicated by thearrow, will be from terminal S2 to S1. This impedance drop is highlyundesirable as it results in noise and distortion in outgoing line L2. v

Now let us see how the provision of the corrective means of the presentinvention, i. e., the path to ground I44 through capacity I45, tends toovercome the above undesirable effect. With the connection of this pathto ground to terminal P2 of the primary winding a component of the noisecurrent will pass through the primary winding to ground I44. Thiscurrent produces an impedance drop in the primary winding which,assuming the same direction of noise voltage as before, will be fromterminal P1 to P2.

2 By transformer action this impedance drop from terminal P1 to P2 ofthe primary will appear across the secondary winding as an impedancedrop from terminal S1 to S2. By proper adjustment of condenser I45 thisdrop from terminal S1 to S2 may be caused to exactly neutralize the dropfrom terminal S2 to S1 caused by the flow of noise current in thesecondary as explained above.

It is possible that under certain conditions the vacuum tube circuit maybe subjected both to longitudinal voltages of the nature discussed abovein reference to Fig. 1 and noise current of the nature discussed inreference to Fig. 2. In such event switch I46 (Fig. 2) may be operatedto contact I55 whereupon condenser I45 will obtain ground throughbattery H1. The windings of input transformer H2 should be rearranged tobe in series aiding relationship when connected P1 to- P2 to S2 to'S1.

The effects of longitudinal noise voltages are neutralized by thismodification of the arrangement described above with reference to Fig. 2in the manner that has been described in detail in reference to Fig. 1while the effects of battery noise voltage are neutralized in a mannergenerally similar to that discussed above in reference to Fig. 2. In thelatter case, a battery noise current will be set up, as explained above,between the primary and secondary windings of input transformer H2 dueto the interwinding capacitances and will produce an impedance drop inthe secondary winding, which, assuming the same noise voltage directionas before, will be from terminal S2 to S1. A current is also set up atthis same time through condenser I45 in the direction from terminal S2to terminal P2. A part of this current will pass through the primarywinding of input transformer H2 in a direction from terminal P2 to-P1.This flow of current causes an impedance drop from terminal P2 to P1which, by transformer action. will appear across the secondary windingas an impedance drop from terminal S1 to. S2. This lastmentionedimpedance drop will act to neutralize the impedance drop from terminalS2 to S1 arising, as explained above, from flow of the noise currentin-the secondary winding.

While specific embodiments of the invention have been selected fordetailed description, the invention is not, of course, limited in itsapplication to the embodiments disclosed; For example, the path toground may include other types of networks than the capacityillustrated. In short, the embodiments described should be taken asillustrative of the invention and not as restrictive thereof.

What is claimed is:

1-. In a. transmission lineincluding a transformer having a primarywinding. anda secondary winding and an inherent. interwinding cadenser,one terminal of' said variable ,conden:

ser being connected to an external; terminal, of, said primary winding,and selective ;means for,

connecting the other terminal of said variable condenser directly toground or to ,ground through said one terminal of the secondary winding.

2. An input transformer for coupling a line to a vacuum tube repeaterhaving a primary winding and a secondary winding, said primary windinghaving a firstexternal terminal and a second external terminal, saidsecondary winding having a first external terminal corresponding to saidfirst terminal of the primary winding and a second external terminalcorresponding to said second terminal of the primary winding, saidwindings being in series-aiding relationship when connected from saidfirst terminal of the primary to said second terminal of the primary tosaid second terminal of the secondary to said first terminal of thesecondary, a connection to ground for an element of the vacuum tuberepeater and said second terminal of the secondary winding and aconnection to ground through a capacitance for said second terminal ofsaid primary, said last-mentioned connection to groundbeing independentof said first-mentioned connection to ground.

3. An input transformer for coupling a line to a vacuum tube repeaterhaving a primary winding and a secondary winding, said primary windinghaving a first external terminal and a second external terminal, saidsecondary winding having a first external terminal corresponding to saidfirst terminal of the primary winding and a second external terminalcorresponding to said second terminal of the primary winding, saidwindings being in series-aiding relationship when connected from saidfirst terminal of the primary to said second terminal of the primary tosaid second terminal of the secondary to said first terminal of thesecondary, a connection to ground for an element of the vacuum tuberepeater and said second terminal of the secondary winding and avariable condenser, one terminal of said variable condenser beingconnected to ground independently of said connection to ground for therepeater element and said second terminal of the secondary winding andthe other terminal of said variablecondenser being connected to saidsecond terminal of the primary winding.

4. In a transmission line subjected tolongitudinal currents, atransformer having a primary winding and a secondary winding, saidprimary winding having a first external terminal and a second externalterminal, said secondary winding having a first external terminalcorresponding to said first terminal of the primary winding and a secondexternal terminal corresponding to said second terminal of the primarywinding, said windings being in series-aiding relationship whenconnected from said first terminal of the primary to said secondterminal of the primary to said second terminal of the secondary to saidfirst terminal of the secondary, and means for neutralizing the effecton said secondary winding of said longitudinal currents, said meanscomprising a connection to ground through a network ior said secondexternal terminal of said primary winding, said connection to groundbeing independent of said secondary winding.

5. In a transmission line subjected to longitudinal currentsatransformer having a primary winding-and a secondary winding, saidprimary winding having a'first external terminal and a second externalterminal, said secondary windinghaving ax first external terminalcorresponding'to said first terminal of the primary winding and a secondexternal terminal corresponding to said second terminal of the primarywinding, said windings being in series-aiding relationship whenconnected from said first terminal of the primary to said secondterminal of the primary to said second terminal of the secondary to saidfirst terminal of the secondary, and means for neutralizing the efiecton said secondary winding of said longitudinal currents, said meanscomprising a path to ground through a variable condenser connected tosaid second external terminal of said primary winding, said path toground being independent of said secondary winding.

6. In a transmission line subjected to longitudinal currents, atransformer having a primary winding, a secondary winding and aninherent interwinding capacitance, said interwinding capacitanceresulting in passage of longitudinal currents from the primary windingto the secondary winding thereby causing a voltage drop in the secondarywinding, means for establishing an independent flow of longitudinalcurrents through the primary winding to ground effective throughtransformer action to establish a voltage rise in the secondary of amagnitude and phase angle ,sufiicient to offset said voltage droptherein.

'7. In a transformer having a primary winding and a secondary winding,one of said windings being subjected to the passage of noise currentstherethrough resulting in an impedance drop therein, means forestablishing an independent flow of noise currents through the other ofsaid windings to ground resulting in an impedance drop therein, themagnitude of said last-mentioned impedance drop being substantially thesame as that of the first-mentioned impedance drop and its directionbeing opposite to that of the first-mentioned impedance drop.

8. In a transformer having a primary winding and a secondary winding,said secondary winding being subjected to the passage therethrough oflongitudinal currents resulting in an impedance drop therein, means forestablishing an independent fiow of longitudinal currents through saidprimary winding to ground resulting in an impedance drop therein, themagnitude of said last-mentioned impedance drop being substantially thesame as that of the first-mentioned impedance drop and its directionbeing opposite to that of the first-mentioned impedance drop.

9. In a transmission line subjected to longitudinal currents, atransformer having a primary winding, a secondary winding and aninherent interwinding capacitance, said interwinding capacitanceresulting in passage of noise currents from one of said windings to theother, a first external terminal and a second external terminal for saidprimary winding, a first external terminal for said secondary windingcorresponding to said first external terminal of said primary, a secondexternal terminal for said secondary winding corresponding to saidsecond terminal of said primary, and means for neutralizing the effecton one of said windings of passage of noise currents through the otherof said windings, said means comprising a path to ground through avariable condenser connected to said second terminal or said primarywinding, said windings being arranged to be in seriesconnected from saidfirst terminal of said primary to said second terminal of said primaryto said first terminal of said secondary to said second terminal of saidsecondary when said noise currents first occur insaidsecondary winding.

EUGENE B. M'ECHLING.

